The present invention relates generally to a drive roller unit for driving articles on a conveyor track.
One form of drive roller unit for driving articles on a conveyor track comprises at least one drive roller which can be driven in rotation by an electric motor assembly, by way of a transmission means, and which in its drive position is in engagement with the underside of the article to be driven thereby. Such drive roller units are employed for example for driving freight containers which are to be movable on roller-type or ball-type conveyor tracks. A preferred area of use of such arrangements are freight loading systems in air freight traffic, in which the containers are transported in the freight compartment of an aircraft on such conveyor tracks until the containers reach the anchorage locations at which they are to be held fast during a flight.
A drive roller unit of the kind referred to above is disclosed for example in U.S. Pat. No. 4,792,037 (Ser. No. 160,427). It comprises a single drive roller which, by means of an electric motor assembly incorporated therein, can firstly be lifted from a lowered rest position in which it is out of contact with an article on the conveyor track until it reaches a raised operative position in which it bears against the underside of the article to be driven thereby for movement on the conveyor track. In the raised position that drive roller can then be driven in rotation by the same electric motor assemby so that it applies to the underside of the article on the track a tangential force which displaces it in a direction substantially normal to the direction of the axis of rotation of the drive roller.
When loading freight containers into the freight compartments of an aircraft, the problem which now arises is that the elongated containers which are frequently longer than the width of the freight compartment of the aircraft must be pushed into the freight compartment with one of their narrow sides leading, through a cargo hatch in the side of the vehicle, and then, when in the freight compartment, turned through 90.degree. so that they can then be moved with their longitudinal axis parallel to the longitudinal axis of the vehicle, until they reach the required anchorage location. For the purposes of introducing the containers through the cargo hatch and for turning them through 90.degree., the floor of the freight compartment was equipped for example in the region of the cargo hatch with a ball-type conveyor track which permits the container to move in all directions and be rotated as indicated above. The ball-type conveyor track included a large number of drive rollers which can be raised and lowered between a rest position and an operative position and which can then be driven in rotation when in the operative position. Suitable control by means of complicated electronic control assemblies meant that such an arrangement could be used to pass the container into the cargo hatch and turned at the same time through 90.degree. during that movement. That operation was effected by the individual drive roller units being selectively raised and lowered; in the lowered condition they performed a rotary movement about a vertical axis while in the raised condition they moved the container forwardly in its turned position.
In practice such an arrangement was found to be complicated and expensive while it also suffered from being of high weight, which is undesirable in the context of air freight traffic, and it was also found to be susceptible to trouble.
In another prior-art construction, more particularly containers of smaller size could be moved manually on the ball-type conveyor track which was disposed in the region of the cargo hatch, and also manually rotated thereon. Instead of ball-type conveyor tracks, some arrangements also employed assemblies of guide rollers which were arranged to cover a suitable area over which the containers were to be moved. It will be seen therefore that the previous arrangements either involved a considerable level of expenditure and complication, to provide for a semi-automated procedure, or it was necessary to use human physical force to effect a container loading operation.